Human to Human (H2H) communication refers to the communication between people, which is implemented by operating equipment. Existing radio communication technology is developed based on the H2H communication. In the H2H communication, people perform communication by means of H2H equipment, that is, User Equipment (UE) in general. While, Machine to Machine (M2M) is defined as communication from a machine to a machine in a narrow sense, and networked application and service with intelligent interaction between machine terminals as a core in a broad sense. The M2M technology is an informatization solution provided for customers with multiple communication modes as access means, based on intelligent machine terminal, to satisfy informatization requirements of the customer on monitoring, commanding and scheduling, data collection and measurement.
The development of radio technology is an important factor for the development of an M2M market. The M2M technology breaks through time and space constraints and geographical barriers of conventional communication mode, so that enterprises and the public can get rid of cable constraints, and customers can control cost more effectively, save installation charge and enjoy simple and convenient usage. In addition, growing requirements are pushing the M2M technology to progress continuously. Contradict with the continuous growth of information processing capability and network bandwidth, the means of information acquisition lags far behind, however, the M2M technology can well satisfy this requirement. Through the M2M technology, external environment can be monitored in time, and large-scale automated information collection can be realized. Therefore, the M2M technology can be widely employed in industry application, household application, personal application and the like, in which the industry application includes traffic monitoring, alarm system, sea rescue, vending machine, driving pay and the like, the household application includes automatic meter reading, temperature control and the like, and the personal application includes life detection, remote diagnosis and the like.
The communication object of the M2M technology is machine to machine, man to machine. Data communication between one or more machines is defined as Machine Type Communication (MTC), in which less man-machine interaction is needed. A machine participating in MTC is defined as an MTC device (MD). The MTC device is a terminal of an MTC user, which can communicate with an MTC device and an MTC server through a Public Land Mobile Network (PLMN).
After M2M application is introduced, existing systems can be optimized according to the feature of the M2M application, so as to meet requirements of the M2M application and not to impact common UEs in the existing systems. Some significant features of the M2M application include: large number of MTC devices, small amount of data transmitted each time, big transmission interval, relatively fixed position and the like. Since the number of MTC device is large, not in the same class as the number of common UE, that is, H2H device, the wide use of MTC device probably could cause an overload state of network, for example, if a cell suffers a power failure event suddenly, when the power is recovered, numerous MTC devices probably could try to access network simultaneously, thus causing an overload state of network.
At present, overload control of a Long Term Evolution (LTE) system is divided into two levels: overload control of an access network and overload control of a core network, in which the overload control of the access network aims at the load of evolved Node B (eNB) only. If the access network has no overload, the request information of a terminal would be sent to the core network; if the core network has overload, the core network returns a reject message to the terminal, then the terminal exits the system and signalling links previously established are released.
For the overload control of the access network, the access of terminal to a system can be controlled through an Access Class Barring (ACB) mechanism. The execution process of the ACB mechanism adopted by the LTE system is introduced below.
Operators define terminal types into 16 Access Classes (ACs), in which AC 0-AC 9 belongs to normal class and is allocated to terminals randomly, AC 10 indicates emergency calls (not allocated to terminals), AC 11 is used for network operations, AC 12 indicates safety services, AC 13 indicates public services (for example, water and gas suppliers), AC 14 indicates emergency services, and AC 15 indicates operator working staff. One terminal can be configured as one class within AC 0-AC 9 and one or more classes within AC 11-AC 15, and the configuration information is stored in a Subscriber Identity Module (SIM) card.
In the LTE system, a system message would broadcast an ACB parameter, through which ACB control can be performed on the emergency call, MO-signalling initiated by a terminal, MO-data initiated by a terminal, Multimedia Language (MMTEL-Voice) and MMTEL-Video. The emergency call can be configured with Barred or Allowed (not barred) only. In other conditions, the network would configure a barring factor and a barring time. The terminal generates a random number between 0 and 1; if the random number is greater than the barring factor, re-access is not allowed within [(0.7+0.6*rand)*ac-barring time], and later the terminal can try to access the system again; otherwise, the terminal is allowed to access the system. In addition, the control on AC 0-AC 9 is the same as the above in the ACM mechanism. For AC 11-AC 15, the network can configure separately whether to bar the access of these classes of users. In the above formula, the rand represents a random number generated by the terminal; and the ac-barring time represents a barring time preconfigured by the system.
If a UE is configured with AC 11-AC 15 and AC 0-AC 9, for the MO data/signalling, it is judged first whether BarringForSpecialAC corresponding to AC 11-AC 15 is barred; if not, the UE accesses the system directly; otherwise, ACB control is performed according to the parameter of AC 0-AC 9. For the emergency call, it is judged first whether ac-BarringForEmergency configured in SIB2 is barred; if not, the UE accesses the system directly; otherwise, it is judged whether the AC corresponding to the ac-BarringForSpecialAC in a data service (ac-BarringForMO-Data) initiated by the barred terminal is barred; if so, the emergency call can not be initiated; otherwise, access is allowed.
After the MTC device is introduced, for preventing impact on a system caused by simultaneous access of large numbers of devices, the ACB mechanism is a very good solution, which can control the time and frequency of a terminal accessing the system, thereby reducing the impact on the system caused by large numbers of terminal from the source. Moreover, since the MTC device generally is of low priority and is delay-insensitive, a strict access control policy can be adopted.
After new service types (or terminal types) are introduced, since these new types generally are considered as delay-insensitive or low-priority services or terminals, in order to fine control and not to impact existing common terminals, it is needed to enhance the existing ACB mechanism, also called Enhanced ACB (EAB). The main enhancement mode includes two modes as follows.
One mode is to extend the number of AC classes, that is, allocate new AC class values for new service types (or terminal types), exceeding the existing 15 classes. The newly allocated AC class can adopt the same control mechanism, but needs to extend the scope of corresponding parameters. For example, add new AC, class 20-class 29 indicates Extended Access Class (EAC) and class 30-class 39 indicates Extended Access Class Low Priority (EAC Low Priority); for the newly added AC, network side can broadcast two sets of different parameters; UEs configured with EAC or EAC Low Priority would neglect broadcast information related to AC 0-AC 9 and AC 11-AC 15.
The other mode is to configure an extra set of parameters for new service types (or terminal types) to perform control in conjunction with the existing AC classes, without extending the number of AC classes: a terminal is configured with a low access priority; network side broadcasts the existing ACB parameters, and meanwhile broadcasts 10 new EACB bits (for normal classes 0-9 information, that is, 10 bits configured in the EACB parameter, in which bit 1 points to a user of AC 0, bit 2 points to a user of AC 1 . . . bit 10 points to a user of AC 9). In the 10 new EACB bits (for normal classes 0-9 information), 0 indicates not barred, and 1 indicates barred; if the first bit is 1, it is indicated that an EAB applicable terminal corresponding to AC 0 is not allowed to have the access. If an EAB applicable UE is configured with AC 0-AC 9, the ACB parameter corresponding to AC 0-AC 9 is neglected and the EAB parameter is used; if the EAB applicable UE is configured with AC 11-AC 15, the EAB parameter is neglected and the ACB parameter corresponding to AC 11-AC 15 is used. The EAB broadcast information consists of: EAB 0-9 bits and EAB applicable UE types. If a UE configured with EAB initiates an emergency call, the UE neglects the EAB information. If the network does not broadcast EAB information, the UE uses the ACB parameter to perform judgment.
In the above EAB scheme, since the EAB parameter is enumerated (Eumm), that is, barred, not barred, once the EAB parameter is configured, the EAB applicable terminal corresponding to some AC(s) would be barred directly or the EAB applicable terminal corresponding to some AC(s) would be allowed directly. If the EAB applicable terminal performs access time control depending on the EAB parameter only, but on the existing ACB mechanism, once this type is allowed to have the access, it is equivalent that the EAB applicable terminal is endowed with a higher priority, this is unreasonable, because the EAB applicable terminal generally is the type of delay-insensitive or low-priority services or terminals. For example, if MTC terminals of AC5 corresponding to EAB are allowed to have the access, then this type of terminals can access system directly; however, normal terminals of AC 5 need to calculate probability according to the ACB parameter, and probably are not allowed to have the access. In this way, it is equivalent that the EAB applicable terminal has a higher priority than the normal terminal; this terminal access is unreasonable, and further system impact could be caused.